The effects of the synthetic non-psychoactive cannabinoid (+)-(3S,4S)-7-hydroxy-delta 6-tetrahydrocannabinol 1,1-dimethylheptyl (HU-211) on the activity of the N-methyl-D-aspartate (NMDA) receptor/ion channel were examined. HU-211 non-competitively blocks the increase in binding of [3H]N-[1-(2-thienyl)-cyclohexyl]piperidine ([3H]TCP) induced by the polyamines spermine and spermidine or by glutamate and glycine. HU-211 does not, however, affect the direct binding of [3H]glycine and [3H]glutamate to their binding sites on the NMDA receptor, which suggests that the effects of HU-211 are not mediated via the binding sites of glutamate-, glycine- and phencyclidine-like drugs or of polyamines. HU-211 can also block 45Ca2+ uptake through the NMDA-receptor/ion channel in primary cell cultures of rat forebrain. All of the above inhibitory effects of HU-211 on the NMDA-receptor/ion channel activity are stereospecific, since the (-)(3R,4R) enantiomer (HU-210) is ineffective.